1. Field of the Invention
This invention relates to an electrophotographic seamless belt such as a belt-form photosensitive member, an intermediate transfer belt, a transfer-transport (image-transferring paper-transporting) belt and a paper transport belt used in electrophotographic apparatus.
2. Related Background Art
Electrophotographic seamless belts are used for electrophotographic apparatus, and are used as, e.g., belt-form photosensitive members, intermediate transfer belts, transfer-transport belts and paper transport belts which are component parts of electrophotographic apparatus.
Electrophotographic seamless belts are commonly comprised of a binder component such as a resin, a rubber or an elastomer in which a resistance control agent has been dispersed to regulate their electrical resistance. The electrical resistance is regulated by methods grouped roughly into the following three types.
(1) A method in which a conductive filler such as carbon black is dispersed in the binder component.
(2) A method in which a surface-active agent is dispersed in the binder component.
(3) A method in which an ion-conductive polymer (polymer-type antistatic agent) is dispersed in the binder component.
The method (1) is a method of regulating electrical resistance which is prevailing in many fields at present, and has such an advantage that the electrical resistance may be hardly affected by temperature and humidity. However, it is very difficult to disperse the conductive filler uniformly in the binder component. Electrophotographic seamless belts resistance-regulated by such a method have sometimes caused faulty images such as blank areas caused by poor transfer and a leak which are due to the scattering of electrical resistance of the belt.
The method (2) can lower surface resistance, but may hardly lower volume resistivity, and have had such a problem that regulating the volume resistivity makes it necessary to add the surface-active agent in a large quantity to cause its bleeding to the surface.
The method (3) has little problems on the scattering of electrical resistance or the bleeding of additives, but can not lower electrical resistance unless the ion-conductive polymer is added in a certain large quantity. This may often cause a problem on its compatibility with the binder component. Especially when a fluorine resin is used as the binder component, the ion-conductive polymer is not well uniformly dispersed in the fluorine resin, so that the resultant belt may have insufficient surface properties and mechanical properties.
In addition, when the electrophotographic seamless belt as described above is used as an intermediate transfer belt or a transfer-transport belt, to the belt surface of which a toner may adhere in some occasions, the releasability of the toner from the belt is still so insufficient as to sometimes cause what is called filming, a phenomenon in which the toner sticks to the belt surface.
In general, polymer-type antistatic agents (ion-conductive polymers) such as polyether-ester amide and polyether amide are considered to form streaky continuous phases in a binder resin and exhibit ionic conduction (semiconduction), and it is known that dispersion of a polymer-type antistatic agent in excess causes a lowering of ionic conduction.
However, when an electrophotographic seamless belt is produced using a resin composition in which the polymer-type antistatic agent is dispersed in streaks, the resultant electrophotographic seamless belt may have so poor surface properties that coarse images tend to be formed when the belt is set in an electrophotographic apparatus and images are reproduced. Also, when the electrophotographic seamless belt is formed by extrusion, there has been such a problem that the polymer-type antistatic agent may orient in streaks in the direction of extrusion (the axial direction of the belt extruded in a tubular form) and the belt tends to split at its ends. Such splitting at the belt ends may remarkably occur when a fluorine resin is used as the binder component of the electrophotographic seamless belt.
Japanese Patent Publication No. 08-007505 discloses a seamless belt formed of a thermoplastic fluorine resin incorporated therein with polyether-ester amide or polyether amide and a sulfonic acid metal salt, but has no disclosure as to surface properties (dispersibility of polymer-type antistatic agent and releasability of toner) and mechanical properties (anti-splitting) of the belt. Nothing is taken into consideration at all on these.
An object of the present invention is to provide an electrophotographic seamless belt having very uniform electrical resistance and superior surface properties and mechanical properties.
The present inventors have made extensive studies taking note of the fact that an ionic-conduction system making use of an ion-conductive polymer (polymer-type antistatic agent such as polyether-ester amide, polyether amide, epichlorohydrin and polyalkylene glycol) is more advantageous than an electronic-conduction system in which the electrical resistance is regulated by dispersing a conductive filler such as carbon black, and that a thermoplastic fluorine resin is used as the binder component of the electrophotographic seamless belt taking account of the releasability of toner.
The present inventors have also made extensive studies on any formulation that enables the polymer-type antistatic agent polyether-ester amide or polyether amide to uniformly disperse in the thermoplastic fluorine resin and at the same time does not lower the ionic conduction (semiconduction). As a result, they have discovered that a seamless belt having very uniform electrical resistance and also having satisfied the surface properties and the mechanical properties can be obtained by mixing in a fluorine resin the polyether-ester amide or polyether amide and a fluorine-atom-containing surface-active agent or halogenated alkali metal salt.
More specifically, the present invention provides an electrophotographic seamless belt containing a thermoplastic fluorine resin, which comprises 3 to 40 parts by weight of a polyether-ester amide or polyether amide and 0.02 to 10 parts by weight of a fluorine-atom-containing surface-active agent or halogenated alkali metal salt, based on 100 parts by weight of the thermoplastic fluorine resin.
The present invention also provides an electrophotographic apparatus comprising the above electrophotographic seamless belt.